The ultimate goal of this project is to develop an innovative in vitro assay for the classification of skin sensitizers that permits evaluation of chemicals within the highly relevant context of a three-dimensional model of human skin that more closely mimics the in vivo environment. Allergic contact dermatitis (ACD) is a wide- spread public health problem resulting from exposure of human skin to certain reactive chemicals in the workplace and in the home. Identifying which chemicals induce ACD is critical to reduce human exposure. There are currently no validated tests for skin sensitization that preclude animal use, yet compelling economic and ethical reasons support development of new in vitro methods that accurately predict the sensitizing potential of a chemical or mixture and eliminate the need for animals. The key technological innovation behind the proposed StrataScreenSENS 96-well assay is a unique three- dimensional human skin model that utilizes luciferase activity as a rapid, easy and accurate quantitative assay readout for skin sensitizing potential. An in vitro assay that provides accurate and robust responses to skin sensitizing chemicals in the context of a human skin model would 1) permit the application of test chemicals to a skin surface, mimicking the actual normal route of exposure in ACD; 2) model the in vivo physiological environment better than the two-dimensional, monolayer culture systems currently employed; 3) utilize a 96- well format to enhance screening throughput; and 4) reduce or replace the need for animal testing in skin sensitizer evaluation. The advantages of StrataScreenSENS directly address the challenges and limitations facing toxicology in the 21st century and speak to the Mission of the National Institute of Environmental Health Sciences. The goals of this Phase I SBIR proposal are to generate and characterize unique cellular reagents for production of the reporter skin model utilized in the StrataScreenSENS assay. This will be accomplished through use of Stratatech's platform technology, the NIKS cells, a consistent source of non-tumorigenic, pathogen-free human keratinocyte progenitors. The ability to genetically engineer NIKS keratinocytes and generate three- dimensional skin tissue that produces exogenous protein provides a unique opportunity to develop reporter skin models responsive to skin sensitizing chemicals. Successful completion of the Phase I Aims will demonstrate the feasibility of our approach and generate the cellular reagents employed in the StrataScreenSENS assay. Subsequent studies will refine assay parameters, supporting validation of an assay that will reduce the risk of public exposure to harmful chemicals and decrease the reliance on animal testing. PUBLIC HEALTH RELEVANCE: Allergic contact dermatitis (ACD) is a wide-spread public health problem resulting from exposure of human skin to certain reactive chemicals in the workplace and in the home. The identification of chemicals which induce ACD is important to reduce human exposure. Similarly, the elimination of tests requiring animals for this identification is important for economic and ethical reasons. Development of a non-animal-based test that identifies chemicals which induce ACD will fill a major need for the pharmaceutical, consumer products, and chemical Industries by decreasing reliance on animal testing and reducing the risk of public exposure to harmful chemicals.